1. Field of the Invention
The present invention relates to a dielectric ceramic composition for use in a high frequency and more particularly to a dielectric ceramic composition which is useful for a material of a dielectric resonator device used at a micro wave band, that is, in a micro wave integrated circuit.
2. Description of Related Art
Recently, mobile communication has spread and a dielectric resonator device is be used as a filter of the base station. Such a dielectric resonator device receives a high power input and so it is necessary to provide a stable dielectric ceramic material resistant to the high power input.
In order to effectively use a limited frequency band, it has been requested to make the frequency band to be more narrow. In response to the requirement, it is desireable to provide a dielectric ceramic material having a high Q value at a high frequency band.
There has been known, for example, a BaO--TiO.sub.2 type material as a dielectric resonator device for a micro wave band, which is generally superior in the dielectric characteristic and has a relatively high Q value at a high frequency band such as the micro wave band.
However, such a BaO--TiO.sub.2 system material comprises two crystal phases, BaTi.sub.4 O.sub.9 and Ba.sub.2 Ti.sub.9 O.sub.20 having thermal expansion coefficients 9 ppm/.degree.C. and 11 ppm/.degree.C., respectively. When the ceramic made of the BaO--TiO.sub.2 system ceramic having both crystal phases included therein is heated, the ceramic generates crack due to a difference of 2 ppm/.degree.C. between both crystal phases in the thermal expansion coefficient. Accordingly, the BaO--TiO.sub.2 system ceramic for use at a high power applied field must be composed of a single phase of either BaTi.sub.4 O.sub.9 or Ba.sub.2 Ti.sub.9 O.sub.20.
Further, in relevant literature of the BaO--TiO.sub.2 material for use in a high frequency, there is offered a paper entitled "The Ternary Systems BaO--TiO.sub.2 --SnO.sub.2 and BaO--TiO.sub.2 --ZrO.sub.2 " J. Am. Ceram. Soc., Vol. 41, No. 10, p.390-394 (1958), in which it is reported that the crystal phase of Ba.sub.2 Ti.sub.9 O.sub.20 can exist stably by substituting Sn or Zr for part of Ti. But, there has no description of the improvement of the dielectric characteristic.
In the Japanese Patent Publication Kokoku sho/56-38007, there is disclosed a Ba--Ti--Mn--Zr system material, in which it is reported that an addition of both Mn and Zr suppresses reduction of a sintered body and prevents the tan .delta. from increasing, but the resultant ceramic body has only a Q value of 6800 at 6 GHz which is not recognized to be sufficiently high.
In the Japanese Patent Publication Kokai sho/62-165805, there is disclosed a Ba--Ti--Ta--Mn system material, in which it is reported that an addition of both Mn and Ta achieves a high Q value, but no addition of Zr results in a problem that the crystal phase stability of Ba.sub.2 Ti.sub.9 O.sub.20 is not sufficient at the high power applied field.